Question

11

Here is an outline for a working class OldCellPhone that has no errors (you may see this exact class several times in this exam):

class OldCellPhone:
   MIN_MEM_CAP, MAX_MEM_CAP = 10, 100000
   MIN_DSCR_LEN, MAX_DSCR_LEN = 10,  100
   DEFAULT_DSCR = "(generic phone)"
   DEFAULT_BOOL = False
   DEFAULT_CAP = 1000   

   # constructor
   def __init__(self, dscr = DEFAULT_DSCR, mem = DEFAULT_CAP,
                cam = DEFAULT_BOOL,  gp = DEFAULT_BOOL):
      """ expcted string, int, 'boolean', 'boolean' """
      if (not self.set_mem_cap(mem)):
         self.mem_capacity = OldCellPhone.DEFAULT_CAP
      if (not self.set_description(dscr)):
         self.description = OldCellPhone.DEFAULT_DSCR
      if (not self.set_camera(cam)):
         self.camera = OldCellPhone.DEFAULT_BOOL
      if (not self.set_gps(gp)):
         self.gps = OldCellPhone.DEFAULT_BOOL
         
   def set_mem_cap(self, mem):
      # def not shown

   def set_camera(self, bool):
      """ member only wants a "boolean" literal, True or False
      (True means 'has cam', False means 'does not have cam' """
      # def not shown

   def set_gps(self, bool):
      """ member only wants a "boolean" literal, True or False
      (True means 'has gps', False means 'does not have gps' """
      # def not shown
   
   def to_string(self):
      # def not shown
      
   # other accessors and mutators not shown

A programmer decides to add an instance method add_memory() whose job it will be to increase the instance attribute mem_capacity by an amount specified by the client as long as the new, increased memory capacity, after adding the amount, is still <= MAX_MEM_CAP. Otherwise, it will not touch mem_capacity.

Check the true statements (there may be more than one correct answer):

a

If correctly defined, a client could add 333 units of memory to the OldCellPhone object, my_cell, by using the syntax: my_cell.add_memory(333)

b

This should be a static or class method.

c

If correctly defined, a client could add 333 units of memory to the OldCellPhone object, my_cell, by using the syntax: OldCellPhone.add_memory( my_cell(333) )

d

This should be an instance method.

e

If correctly defined, a client could add 333 units of memory to the OldCellPhone object, my_cell, by using the syntax: OldCellPhone.add_memory(333)

Answer 1

The correct options is a and d.
add_memory() as defined in the description is given as an instance method so that automatically rules out any possibility of it being static and so all the options pertaining to static is automatically ruled out (Option b, c and e).
Just for clarification: - Major difference b/w static and instance methods is that instance methods operate on every new instances of classes (objects). So options a and d are valid in this case.
- Static methods doesn't require any new class instances altogether for them to work. Options b and e are valid in case of static methods, are ruled out in our case.
- Option c is altogether invalid with OldCellPhone.add_memory( my_cell(333) ). Since in constructor definition of OldCellPhone class, we have no definition that allows for operating only with inputted memory value as a constructor parameter.